lib/Target/WebAssembly/WebAssemblyOptimizeReturned.cpp

   1 //===-- WebAssemblyOptimizeReturned.cpp - Optimize "returned" attributes --===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 ///
   9 /// \file
  10 /// Optimize calls with "returned" attributes for WebAssembly.
  11 ///
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "WebAssembly.h"
  15 #include "llvm/IR/Dominators.h"
  16 #include "llvm/IR/InstVisitor.h"
  17 #include "llvm/Support/Debug.h"
  18 #include "llvm/Support/raw_ostream.h"
  19 using namespace llvm;
  20
  21 #define DEBUG_TYPE "wasm-optimize-returned"
  22
  23 namespace {
  24 class OptimizeReturned final : public FunctionPass,
  25                                public InstVisitor<OptimizeReturned> {
  26   StringRef getPassName() const override {
  27     return "WebAssembly Optimize Returned";
  28   }
  29
  30   void getAnalysisUsage(AnalysisUsage &AU) const override {
  31     AU.setPreservesCFG();
  32     AU.addRequired<DominatorTreeWrapperPass>();
  33     AU.addPreserved<DominatorTreeWrapperPass>();
  34     FunctionPass::getAnalysisUsage(AU);
  35   }
  36
  37   bool runOnFunction(Function &F) override;
  38
  39   DominatorTree *DT = nullptr;
  40
  41 public:
  42   static char ID;
  43   OptimizeReturned() : FunctionPass(ID) {}
  44
  45   void visitCallSite(CallSite CS);
  46 };
  47 } // End anonymous namespace
  48
  49 char OptimizeReturned::ID = 0;
  50 INITIALIZE_PASS(OptimizeReturned, DEBUG_TYPE,
  51                 "Optimize calls with \"returned\" attributes for WebAssembly",
  52                 false, false)
  53
  54 FunctionPass *llvm::createWebAssemblyOptimizeReturned() {
  55   return new OptimizeReturned();
  56 }
  57
  58 void OptimizeReturned::visitCallSite(CallSite CS) {
  59   for (unsigned I = 0, E = CS.getNumArgOperands(); I < E; ++I)
  60     if (CS.paramHasAttr(I, Attribute::Returned)) {
  61       Instruction *Inst = CS.getInstruction();
  62       Value *Arg = CS.getArgOperand(I);
  63       // Ignore constants, globals, undef, etc.
  64       if (isa<Constant>(Arg))
  65         continue;
  66       // Like replaceDominatedUsesWith but using Instruction/Use dominance.
  67       Arg->replaceUsesWithIf(Inst,
  68                              [&](Use &U) { return DT->dominates(Inst, U); });
  69     }
  70 }
  71
  72 bool OptimizeReturned::runOnFunction(Function &F) {
  73   LLVM_DEBUG(dbgs() << "********** Optimize returned Attributes **********\n"
  74                        "********** Function: "
  75                     << F.getName() << '\n');
  76
  77   DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
  78   visit(F);
  79   return true;
  80 }